Final answer:
The left hemisphere might be most active when answering the question 'what do the following words have in common: plane, butter, insect?'
Step-by-step explanation:
The brain structure that might be most active when answering the question 'what do the following words have in common: plane, butter, insect?' is the left hemisphere.
Studies have shown that language functions, such as comprehension and production of speech, are usually localized in the left hemisphere of the brain. This hemisphere is responsible for processing and understanding linguistic information.
Therefore, when a person is asked to find the commonality between words like 'plane, butter, insect,' their left hemisphere would likely be most active in processing the linguistic aspects and making connections between these words.